Flaxseed may not cool hot flashes

NEW YORK (Reuters Health) - Despite some promising early evidence, a new clinical trial suggests that flaxseed may not ease menopausal hot flashes after all.

In a study of 188 women, researchers found those who were randomly assigned to eat a daily flaxseed bar saw no more improvement in their hot flashes than women given flax-free "placebo" bars.

Over six weeks, more than one-third of women in each group had a 50 percent reduction in their hot flash "score" -- which measures the frequency and severity of a woman's symptoms. The similar results in both groups suggest a placebo effect or some other explanation for the changes some women reported, researchers said.

"What women should take from this study is that there is little compelling information to try flaxseed if the objective is to reduce hot flashes," senior researcher Debra L. Barton told Reuters Health in an email.

In an earlier pilot study, Barton and her colleagues at the Mayo Clinic in Rochester, Minnesota, had found that women who consumed flaxseed did see their hot flashes wane, on average.

But that study had no comparison group of women taking a placebo, Barton pointed out.

Flaxseed is high in compounds called lignans, a type of phytoestrogen. These are plant chemicals structurally similar to estrogen and may have weak estrogen-like (and anti-estrogen) activity in the body.

The most effective treatment for hot flashes is hormone replacement therapy. But since hormones have been linked to increased risks of heart disease, blood clots and breast cancer, many women want alternative hot-flash remedies.

Some antidepressants have been found to cool hot flashes by as much as 80 percent. But "natural" products, Barton noted, have generally failed to stand up to the test of clinical trials. Those products include black cohosh, soy and now flaxseed.

The current study, reported in the journal Menopause, included women with bothersome hot flashes -- occurring at least an average of four times a day.

Half of the women had a history of breast cancer -- which would generally make it inadvisable to use hormones to treat hot flashes.

Barton's team randomly assigned the women to eat either a flaxseed bar or a placebo bar everyday for six weeks. The flaxseed bar contained fiber, protein and 410 milligrams of lignans; the placebo bar provided protein and fiber, but no lignans.

By the end of the study, there was no difference between the two groups in hot-flash symptoms -- which the women recorded in a daily diary.

In both groups, 36 percent of women had a 50 percent drop in their hot-flash scores. And when asked to rate their hot flashes, one-third of women in each group said they thought their symptoms were moderately to "very much" improved.

There are several potential reasons for the findings, Barton said.

In general, she explained, studies into hot flashes have found a significant placebo effect -- where women feel better because they expect to. Overall, 20 percent to 30 percent of placebo users improve, Barton noted -- though some studies have found even higher rates.

On top of that, hot flashes naturally cool off over time for some women. And, Barton said, they can be "extremely variable" since environmental triggers often set them off -- like hot weather or stress.

"This is why it's important to perform randomized, placebo-controlled trials to understand the potential risks and benefits of interventions," Barton said.

Flaxseed may be helpful for other health issues, like constipation, Barton noted. But as a hot-flash remedy, the evidence is lacking, she said.

As for side effects, the researchers found that women in both groups commonly reported abdominal bloating and gas -- probably because of the fiber in both types of bar.